What is the difference between RNA and DNA in the context of cancer testing?

DNA (deoxyribonucleic acid) is the stable, double-stranded genetic blueprint of every cell. RNA (ribonucleic acid) is a single-stranded molecule that carries information from DNA to the protein-making machinery. MicroRNA is a special class of RNA that regulates which genes are active. Cancer testing based on DNA typically looks for mutations (changes in the genetic sequence) or methylation patterns in circulating tumor DNA (ctDNA). Cancer testing based on RNA — specifically miRNA — looks for changes in gene regulation signals rather than structural mutations. MiRNA changes are often detectable earlier in the cancer process because they precede the accumulation of ctDNA mutations to levels detectable in blood or urine.